1. Field of the Invention
The present invention relates to a structure to join a cylinder lifting a cargo-handling tool, more specifically to a structure to join a cylinder which is joined to a connecting member which connects a pair of right-hand and left-hand second masts to each other, and which is used for vertically moving the cargo-handling tool provided on the pair of right-hand and left-hand second masts being vertically moved with respect to a pair of right-hand and left-hand first masts provided on a forklift truck
2. Description of the Related Art
Cargo-lifting mechanisms of a type having a structure as schematically shown in FIG. 1 are known, that is, a cargo-lifting mechanism having three pairs of masts provided with a free lift. The foregoing lifting mechanism incorporates a pair of right-hand and left-hand (in a direction perpendicular to the surface of a drawing sheet) outer masts 1 secured to a front portion of the forklift truck. A pair of right-hand and left-hand middle masts 3 are provided for the outer masts 1 such that vertical movement of the middle masts 3 is permitted. Moreover, a pair of right-hand and left-hand inner masts 5, which are capable of moving vertically, are provided for the middle masts 3. The inner masts 5 are provided with a fork 7 serving as a cargo-handling tool on which a cargo is placed such that vertical movement of the fork 7 is permitted.
A cargo-handling-tool lifting cylinder (a full-free cylinder) 9 for vertically moving the fork 7 is secured to a position adjacent to the inner masts 5. The fork 7 and the inner masts 5 are connected to each other by dint of a chain 15 through a chain sprocket 13 disposed at the top end of a cylinder rod 11 of the cargo-handling-tool lifting cylinder 9. When the cargo-handling-tool lifting cylinder 9 is operated, the fork 7 is vertically moved with respect to the inner masts 5.
On the other hand, mast-lifting cylinders 17 for vertically moving the middle masts 3 and the inner masts 5 are disposed at positions adjacent to the outer masts 1. The outer masts 1 and the inner masts 5 are connected to each other by dint of a chain 21 through chain sprockets 19 disposed on the upper portions of the middle masts 3. When the middle masts 3 are moved vertically because of the operation of the mast-lifting cylinders 17, the inner masts 5 are moved vertically with respect to the outer masts 1 for a distance that is twice that of the middle masts 3 is vertically moved.
FIG. 2 is a plan view showing a specific structure of the above-mentioned lifting mechanism. The lower ends of the pairs of the right-hand and the left-hand outer masts 1, middle masts 3 and the inner masts 5 are connected to each other by an outer-mast lower beam 23, a middle-mast lower beam 25 and an inner-mast lower beam 27. The pair of right-hand and left-hand mast-lifting cylinders 17 for vertically moving the middle masts 3 are elongated vertically on the outer-mast lower beam 23 disposed in the rear of the outer masts 1. On the other hand, the cargo-handling-tool lifting cylinder 9 for upwardly moving the fork 7 is elongated vertically on a cylinder support 29 which is disposed between the right-hand and left-hand inner masts 5 and which forwards projects over the inner-mast lower beam 27.
The fork 7 is joined to the front surface of a carriage 33 secured to the leading ends of a pair of carriage brackets 31 disposed on the inside of the inner masts 5. Mast rollers 35 are joined to the side surfaces of the upper and lower ends of the carriage brackets 31. When the mast rollers 35 vertically roll with respect to the inner masts 5, the carriage brackets 31, the carriage 33 and the fork 7 are vertically moved with respect to the inner masts 5. Mast rollers (not shown in FIG. 2) are disposed between the outer masts 1 and the middle masts 3 and between the middle masts 3 and the inner masts 5 (for example, mast rollers 36 are disposed in the lower portions of the inner masts 5 as shown in FIG. 3 to be described later).
Lift-mechanism support brackets 37 for mounting the foregoing lifting mechanism on the forklift truck (a front axle shaft) are disposed at the right and left ends of the outer-mast lower beam 23. The distance from the joining center of each of the lift-mechanism support brackets 37 to the carriage 33 is a front overhang (FOH). When the FOH is reduced, the distance from the forklift truck to a portion for holding a cargo can be shortened. Thus, a cargo-handling operation can stably be performed.
FIG. 3 is a perspective view showing the inner masts 5 and the cargo-handling-tool lifting cylinder 9 which is joined to the inner masts 5. A threaded hole 29a is formed in the upper surface of the cylinder support 29 provided for the inner-mast lower beam 27. A bolt 39 is screwed in the threaded hole 29a. On the other hand, a locating recess 9a into which the head of the bolt 39 is introduced is formed in the lower surface of the cargo-handling-tool lifting cylinder 9.
In a state in which the locating recess 9a of the cargo-handling-tool lifting cylinder 9 is received by the head of the bolt 39 jointed to the upper surface of the cylinder support 29, brackets 41 disposed at positions relatively upper than the central portion of the cargo-handling-tool lifting cylinder 9 are secured to a center beam 43 with two bolts 45, the center beam 43 establishing the connection between intermediate portions of the inner masts 5 in the vertical direction. Thus, the cargo-handling-tool lifting cylinder 9 is joined to a position adjacent to the inner masts 5.
FIG. 4 shows an example in which two cargo-handling-tool lifting cylinders 9 are employed. The cylinders 9 are disposed at positions adjacent to the right and left inner masts 5. In the foregoing example, pins 47 disposed on a cylinder support 29 are received by recesses 9a formed in the lower surface of the cargo-handling-tool lifting cylinder 9. In the foregoing state, brackets 41 provided for the cargo-handling-tool lifting cylinder 9 are secured to the center beam 43 with bolts 45.
The example of the structure for joining a cylinder for lifting a cargo-handling tool of the type shown in FIG. 3 has the arrangement that the cargo-handling-tool lifting cylinder 9 is disposed at an intermediate position between the right and left inner masts 5. Therefore, forward visibility is unsatisfactory for an operator of the forklift truck to efficiently perform the cargo handling operation. The example shown in FIG. 4 incorporates the two cargo-handling-tool lifting cylinders 9 disposed at the right and left positions. Therefore, the forward visibility is improved as compared with the example shown in FIG. 3. However, the cargo-handling-tool lifting cylinders 9 are disposed between the carriage brackets 31 shown in FIG. 2. Therefore, the visibility for the forklift operator is obstructed. Thus, further improvement in the visibility is required.
To improve the forward visibility, a structure is disclosed in Japanese Utility-Model Applications Laid-Open No. 57-155198 and Laid-Open No. 59-123096. The structure is formed such that cargo-handling-tool lifting cylinders 9 are disposed adjacently to inner masts 5 at positions in the rear of the inner masts 5.
When the cargo-handling-tool lifting cylinders 9 are disposed adjacently to the inner masts 5 at positions in the rear of the inner masts 5, a structure may be employed in which brackets 41 for securing the cargo-handling-tool lifting cylinders 9 are, as shown in FIG. 5 which is a plan view, secured to the center beam 43 by dint of bolts 45 from front positions of the forklift truck. To improve the forward visibility by disposing the cargo-handling-tool lifting cylinders 9 at further outer positions in the widthwise direction of the forklift truck, heads of the bolts 45 interfere with the inner masts 5. Therefore, satisfactorily improved forward visibility cannot be obtained.
To reduce the front overhang (FOH), the cargo-handling-tool lifting cylinders 9 must be disposed at positions closer to the center beam 43. If the distance is too short, the leading end of the bolts 45 screwed in the brackets 41 interfere with the cargo-handling-tool lifting cylinders 9. To prevent the interference, the distance between the two bolts 45 must be elongated. Moreover, the cargo-handling-tool lifting cylinders 9 must be disposed closer to the central portion. If the distance between the bolts 45 is elongated, the size of each of the brackets 41 is enlarged excessively to easily handle the brackets 41. What is worse, the forward visibility deteriorates. As a matter of course, the forward visibility deteriorates if the cargo-handling-tool lifting cylinders 9 is disposed adjacent to the central portion.
The above-mentioned structure in which the cargo-handling-tool lifting cylinders 9 disposed adjacent to the inner masts 5 and in the rear of the inner masts 5 is secured from the front positions of the forklift truck with the bolts 45 cannot permit a satisfactorily wide forward visibility to be obtained. If the cargo-handling-tool lifting cylinders 9 are disposed closer to the center beam 43 in order to satisfy the FOH, the forward visibility furthermore deteriorates. Therefore, an improvement is required.